This invention relates to bus systems for electrical distribution and relates particularly but not exclusively to bus ducting systems and to apparatus for bus take off connections.
Most presently known and used bus bar and bus bar duct systems are bulky due to the presence of airways along the ducts. These airways provide electrical clearance of the bus bars and cooling is effected wholly or partly by convection. Such cooling by convection is not an efficient or quick method of heat dissipation from the bus bars. Another reason for the bulkiness of presently known and used systems is the necessity to provide mechanical reinforcement of the bus bars to restrain the bars against violent deformation should a short circuit or overload cause reactance between neighboring bus bars. This reinforcement is usually effected by means of discrete insulating supports within the duct or by continuously wrapping a group of bus bars with an insulating material of suitable strength. Such methods invariably include additional air pockets, large or small, which result in convection heat transfer from the bus bars when heating occurs. Furthermore, known bus bar systems have lower current ratings due to low contact pressures between serially connected bus bar lengths or great cost due to the necessity to e.g. tin plate the joining tongues of bus bars.
It is the object or objects of this invention to reduce or overcome some or all of the disadvantages of the currently used bus bars and/or bus bar duct systems.
The present invention therefore provides in one preferred form a bus bar and duct combination comprising a plurality of bus bars encased and held, at a central part between end joint parts of the bus bars, within a metal duct such that the bus bars, the duct and electrical insulation members are in intimate contact to provide heat transfer from the bus bars to the duct by way of conduction. Furthermore the duct provides full mechanical support for the bus bars and thus internal reinforcement means are not required. Preferably the bus bars are substantially entirely made of copper or aluminium and the duct is of extruded aluminium having a plurality of integrally formed cooling fins around at least a major portion of the periphery of the duct. Preferably the duct is formed of two, or two pairs of, symmetrical substantially U shaped cross-sectional complimentary duct sections. Preferably the bus bars and duct are separated from one another by individual electrically insulating members. Preferably the combination includes a separate extruded rubber sealing and electrically insulating member between the sides of the bus bars and the sides of the duct which interleave with the insulating members between and extending laterally of the individual bus bars. Preferably the insulating member between the bus bars or bus bars and the duct consists of a plurality of sheets but may consist of a single insulating sheet. Preferably, one or more bus bar and duct combination(s) are adapted for modulator interconnection or coupling.
The present invention also provides a bus to the duct combination comprising a plurality of bus bars encased and held, at a central part between end joint parts of the bus bars, within a metal duct such that the bus bars, the duct and electrical insulation members are in intimate contact to provide heat transfer from the bus to the duct by way of conduction in which the duct is formed of constant cross-section extruded metal duct sections. Preferably the metal of the duct sections is aluminium or aluminium alloy. Preferably the duct sections have a plurality of integrally formed cooling fins around the periphery of the duct formed from the duct sections to enhance radiation of heat from the combination and to increase the mechanical strength of the combination to guard against mechanical failure of the combination in the event of an electrical overload when a plurality of bus bar and duct combinations are used in an electrical supply system.
Further the invention provides a bus bar and duct combination as described above in which the joint sections are adapted for coupling with other bus bar and duct combination(s) and is provided by splaying of the bus bars external of each end of the duct to form substantially parallel spaced bus bar sections which can be interleaved with another bus bar and duct combination in series. Modular bar and duct combinations facilitate interconnection with other bus bar and duct combinations. Appropriate insulation is provided at the joint section between the , pairs of bus bar joint sections. Preferably the bus bars have laterally extending U shaped slots therein to accommodate appropriate joint holding means such as bolts and nuts. Preferably the joint is covered above and below by suitable insulating means and cover plates. Preferably the joint is covered on each side and strengthened against movement or deformation by means of suitable fish or joining plates. Preferably there is provided additional means to connect each bus bar duct combination to provide appropriate earthing of the combination.